1. Field of the Invention
The present invention relates to an ink jet recording method, and more particularly to an ink jet recording method wherein a reaction solution and an ink composition are deposited onto a recording medium to conduct printing. The present invention also relates to an ink composition suitable for use in the ink jet recording method.
2. Background Art
Ink jet recording is a printing method wherein droplets of an ink composition are ejected and deposited onto a recording medium such as paper to conduct printing. This method has a feature that an image having high resolution and quality can be printed at a high speed by means of a relatively inexpensive apparatus. In general, the ink composition used in the ink jet recording comprises water as a main component and, added thereto, a colorant and a wetting agent, such as glycerin, for preventing clogging.
Inks used in the ink jet recording are required to have properties including that the ink does not undergo any change in properties during storage, does not clog nozzle holes of the print head, does not yield an unacceptable image due to color-to-color intermixing (hereinafter referred to as "color bleeding") in an area where inks of different colors are superimposed on top of each other or one another, can yield a high-density image, and can yield an image possessing rubbing/scratch resistance, lightfastness, and waterfastness. Although water-soluble dyes have been mainly used as colorants for the ink in the above methods, utilization of inks using pigments has been proposed from the viewpoint of improving the lightfastness and the waterfastness of the printed image.
The image yielded by the ink composition using a pigment certainly possess excellent waterfastness. Since, however, the pigment is generally insoluble in water, it is necessary to stably disperse pigment particles in the ink composition. When the state of dispersion of the pigment in the ink composition is unstable, precipitates and the like are likely to be created, often clogging nozzles of the ink jet printing head. An additional problem associated with the ink composition using a pigment is that the ink composition using a pigment is inferior to that using a dye in rubbing/scratch resistance of the printed image because the pigment is basically present as particles on the recording medium. In order to solve the problems involved in the ink composition using a pigment, the addition of an inorganic oxide colloid, such as colloidal silica, to the ink composition has been proposed in the art (for example, Japanese Patent Laid-Open No. 199780/1984).
Regarding the ink jet recording method, the application of a polyvalent metallic salt solution onto a recording medium followed by the application of an ink composition containing a dye having at least one carboxyl group has been recently proposed (for example, Japanese Patent Laid-Open No. 202328/1993). The claimed advantage of this method is that the polyvalent metal ion combines with the dye to form an insoluble complex, the presence of which can offer an image having waterfastness and high quality free from color bleeding.
Further, the use of a color ink comprising at least a surfactant for imparting a penetrating property or a solvent having a penetrating property and a salt in combination with a black ink capable of being thickened or agglomerated through the action of the salt has been proposed to yield a high-quality color image having a high image density and free from color bleeding (Japanese Patent Laid-Open No. 106735/1994). Specifically, an ink jet recording method has been proposed wherein two liquids, a first solution containing a salt and a second solution of an ink composition are printed to yield a good image.
Ink jet recording methods using two liquids are disclosed also in, for example, Japanese Patent Laid-Open Nos. 240557/1991 and 240558/1991.
In the above ink jet recording methods wherein two liquids are printed, a further improvement in the following properties has been desired in the art.
At the outset, an improvement in fixability of the colorant is required. In recent years, recycled papers have become used instead of wood free papers. In many cases, for the recycled papers, the penetration of an ink is better than that for the wood free papers. For this reason, a high-quality image is formed on the wood free papers, whereas feathering or color bleeding is often created in the image formed on the recycled papers, so that, for recycled paper, the elimination of the feathering or color bleeding has been desired in the art.
Secondly, a reduction in uneven printing is required. The uneven printing refers to a variation in color density in the print derived from localization of a colorant on the paper. Although the uneven printing poses no significant problem in printing of letters of regular size, it is a serious problem in applications where figures, graphs and the like are printed.
Thirdly, broadening the range of usable colorants is required. Most of ink jet recording methods where two liquids are printed utilize a salting-out phenomenon between a metal ion and a carboxyl ion contained in the colorant. Therefore, the colorant should have a carboxyl group. Some dyes, however, contain a group other than the carboxyl group, for example, a group which has been water-solubilized by the action of a sulfonic group. A recording method which permits the utilization of such dyes has been desired in the art.